The present invention relates broadly to a counting circuit, and in particular to a tallying circuit for counting the number of logical ones in an input.
Counting circuits may comprise any of several types of functional circuits which are used in the switching or digital data-processing systems, such as dial telephone systems and digital computers. The general function of a counting circuit is to receive and count repeated current or voltage pulses, which represent information arriving from some other circuit within the same system or from a source external to the system. Counting circuits may be devised with a variety of switching circuit devices, such as electromagnetic relays, vacuum tubes, and transistors.
The basic requirement of a counting circuit is to detect each incoming pulse and to establish within itself a unique state for each successive appearance of such a pulse. The number of pulses that have arrived can then be indicated to another circuit by an output which reflects the particular state of the counting circuit.
Obviously, the simplest counter is one that counts only a single pulse. With electromagnetic relays the counting of a single pulse requires at least two relay actions, one to record the arrival of the input signal, and a second to record its disappearance. A simple binary counter may utilize a pair of transistors in a flip-flop circuit arrangement. In this type of circuit, the rest or the normal (no count) state is designated by one transistor conducting, while the other transistor is cut off. The first positive input pulse will be applied to the base of the conducting transistor (first) which causes it to cut off and the other transistor (second) to conduct. The second positive input pulse will now pass to the base of the second transistor (conducting) causing it to cut off and causing the first transistor (cut off) to conduct. After two input pulses, therefore, the circuit is back to its normal state.